1. Field of the Invention
The present invention relates to flat panel speaker units and electronic devices, such as mobile telephones, provided with the flat panel speaker units.
2. Description of Related Art
A known flat panel speaker that is arranged in front of a display device for mobile telephones or the like has the following configuration. FIG. 15 is a perspective view illustrating the conventional flat panel speaker, arranged in front of a display device, FIG. 16 is a cross-sectional view of the flat panel speaker, taken along line B-B in FIG. 15, and FIG. 17 is an enlarged view illustrating a portion C in FIG. 16 (cf. Japanese Utility Model No. 3078022).
The conventional flat panel speaker is furnished with a transparent diaphragm 2 and vibration generating parts 4 for vibrating the diaphragm 2, each provided corresponding to one end of the diaphragm 2. Each of the vibration generating parts 4 comprises a magnet unit 41 and a coil 40 provided on the diaphragm 2. The magnet unit 41 comprises a case 44, a yoke 43, and a magnet 42 covered by the yoke 43.
By passing an electric signal based on an audio signal through the coil 40, magnetic flux is produced from the coil 40. The magnetic flux interacts with the magnetic field of the magnets 42, 42, causing the diaphragm 2 to vibrate up and down. This causes the diaphragm 2 to output sound.
The above-described flat panel speaker is configured such that the transparent diaphragm 2 is mounted on a chassis 8 of the electric device, such as a mobile telephone, through a cushioning material 19, and that a display device 3, which is a liquid crystal panel, is provided below the diaphragm 2. The chassis 8 has a window 18 facing the diaphragm 2 and the display device 3. Thus, the user can view the image on the display device 3 through the diaphragm 2.
The conventional flat panel speaker, however, has the following problems to be resolved.
1. Currently, electric devices such as mobile telephones are required to have a thinner chassis 8. Accordingly, it is preferable that the gap between the diaphragm 2 and the display device 3 be narrowed. In the conventional electric devices, however, the flat panel speaker and the display device 3 are separately mounted in the chassis 8. This makes it difficult to control the vertical gap between the diaphragm 2 and the display device 3 in the manufacturing process of the electric device, leading to such drawbacks as that the diaphragm 2 and the display device 3 come into contact with each other.
2. Having to be arranged in front of the display device, the diaphragm 2 has a flat central portion so that the image viewed through the diaphragm 2 does not deform. For this reason, the central portion of the diaphragm 2 is weak in strength. Moreover, the diaphragm 2 is uncovered in the conventional display device and is therefore susceptible to breakage caused by pressure or impact from the outside. If the diaphragm 2 is made thicker, the diaphragm 2 will have an increased strength against pressure and impact but will become difficult to vibrate, resulting in poorer sound quality.
3. According to the conventional configuration shown in FIG. 17, the coil 40 is arranged in a gap between the yoke 43 and the magnet 42. This means that the size of the coil 40 cannot be larger than the gap, which risks the vibration of the coil 40 not passing sufficiently into the diaphragm 2. Moreover, there is also a concern that the yoke 43 and the coil 40, or the coil 40 and the magnet 42, scrape on each other in manufacturing the flat panel speaker.